Research On Salt-Seeding Numerical Simulations In Convective Cloud

A convective precipitation is simulated using a3-D convective cloud salt-seeding model, considering the microphysical processes between salt particles, liquid and ice particles. The following conclusion can be drawn from simulation results.Simulation results of Qing Hai province indicate that rainfall amount can be enhanced with appropriate seeding methods. In this test, seeding at10th minute in three times with two minutes interval using seeding particle size of20μm can produce a better seeding effect, which will achieve27%precipitation enhancement. Increasing seeding times will reduce precipitation. Further verification tests of salt particle size show that, if only change the particle size,23μm can achieve maximum precipitation enhancement effect, reaching32%. Choosing higher cloud base temperature case in Hu Bei province, the same deeding methods are effective in rainfall enhancement; furthermore, the seeding effect will teach53%. Natural precipitation will decrease with increased dNdB. Increasing initial number of ice crystals in cloud will decrease precipitation.Seeding will cause change of many microphysical source terms. Graupel melting into rain is the main mechanism of raindrop formation, graupel collection of raindrop is the main mechanism of graupel increasing. These two processions are increased after seeding. Seeded salt particles can be used as embryos for raindrop, leading to delay of automatic conversion of cloud to rain and the conversion rate is decreased.Salt particles seeding will change mixing ratios of hydrometeors. Overall, salt particles absorb cloud water to form salt drops causing rapid reduction of cloud water mixing ratio; the rates of ice collecting rain reduce and ice mixing ratio increase. Because of increase rates of graupel melting into rain, graupel mixing ratios are reduced and rain mixing ratios are increased comparing to natural cloud. Rain mixing ratio change because of seeding appear latest among all hydrometeors.Comparing with natural cloud, average radium of graupel increase in the seeded cloud, which indicates salt seeding will influence cold rain process. The mixing ratio of graupel around seeding area and mixing ratio of rain near ground have apparent growth. Dynamic fields in seeding cloud also show updrafts enhancement on cold area; radar echos of seeding cloud in the mature stage are enhanced comparing with natural cloud.